The Morphology and Surface Area of Emulsion derived (PolyHIPE) Foams Prepared with Oil-phase Solubile Porogenic Solvents 2: Three-component Surfactant System

The influence of organic-soluble porogenic solvents (toluene, chlorobenzene, (2-chloroethyl)-benzene, 1,2-dichlorobenzene, and 1-chloro-3-phenylpropane) on the morphology and microstructure of poly(divinylbenzene) emulsion-derived (PolyHIPE) solid foams prepared with a three-component surfactant system is described. It is found that all solvents employed apart from 1,2-dichlorobenzene (C2B) lead to much higher surface areas than corresponding solid foams prepared with SPAN 80 as surfactant. Experiments where the emulsion droplet phase volume is varied indicate that Ostwald ripening is much reduced with the three-component surfactant system compared to SPAN 80, and this is the likely cause of the higher surface areas. The lesser extent of Ostwald ripening is also suggested by NMR water selfdiffusion experiments, which indicate a lower diffusion coefficient when the mixed surfactant is used. The peculiar behavior of C2B is ascribed to its presumed effect on the packing of surfactant molecules at the interface; the 1,2-substitution pattern may produce a strong steric effect, thus allowing greater contact between the aqueous and organic phases.